The number of portable electronic devices is ever increasing these days.
The electronic devices are typically powered from an external power supply via wired connection. However, it is not practical for the user to always receive power through the wired connection. Since various electronic devices have different power requirements, most of the electronic devices are provided with their own dedicated power supplies. As a result, there exist various kinds of numerous power supplies dedicated to the respective electronic devices.
In the meantime, many portable electronic devices are powered by batteries. Frequent use of the portable electronic devices often makes the batteries easily depleted. However, the use of the batteries will avoid the need for a wired connection to a power supply during the use of the electronic device. Again, however, since the batteries lose their power from the use of the devices, they will need recharging (or replacing). To provide a significantly improved user experience, a power supply for wirelessly supplying power to electronic devices by means of microwaves has been proposed. The microwave power transmission enables wireless power transfer to the electronic devices without requiring any wired connection.
The efficiency of wireless power transmission depends on sizes of the power receiver (RX) and transmitter (TX) and a distance between the RX and the TX. Transmitted microwaves considerably diverge with increasing distance between the TX and the RX. The divergence rate of microwaves is determined by relations between transmitting aperture size, distance, and operating wavelength. To approximately estimate the achievable efficiency, an RX antenna aperture is denoted as DRx, and DTX denotes an equivalent TX aperture size recalculated for the receiver position. The equivalent aperture DTX is determined in such a way to include the main power flux emanating from a TX antenna. The efficiency η of power transmission is proportional to ratio of the square of RX antenna aperture to the square of equivalent TX antenna aperture (η˜DRX2/DTX2). FIGS. 1A and 1B show comparison of power transmission efficiency depending on the distance between TX and RX antennas, the TX antenna being small. Specifically, FIG. 1A shows high efficiency at a short distance between the TX and RX antennas, and FIG. 1B shows low efficiency at a long distance between the TX and RX antennas. More specifically, when the TX antenna is small, the efficiency η of power transmission is high as the distance between the TX and RX antennas becomes short. However, as the distance between the TX and RX antennas increases, the efficiency η of power transmission drops very fast because of intense field divergence.
On the other hand, for a large TX antenna as shown in FIG. 1C, field divergence is lower than that of the small antenna shown in FIGS. 1A and 1B. Accordingly, with the large TX antenna, the efficiency η of power transmission drops slowly as the distance between the TX and RX antennas increases. It stays on a moderate level even when TX and RX antennas are close to each other (see FIG. 1C). Assessment of the efficiency η of power transmission is based on assumption of divergent electromagnetic waves. As shown in FIGS. 1A through 1C, by providing radiating waves converging from TX to RX, the received power and thus the efficiency η may be sufficiently increased. This effect is referred to as electromagnetic waves focusing phenomena, and may be employed in microwave wireless charging systems.
For effective power transmission from TX to RX antennas, TX system can be provided with information about an RX antenna position relative to TX antenna. One method to obtain this information is to elaborate preliminary RX search by TX system providing a narrow beam of radiated electromagnetic power. If a TX implements beam steering for a nearby RX, there is no difference in received power, because for different scanning angles (e.g., FIGS. 2A and 2B) the receiver absorbs the same rate of microwave power. The TX selects an angle for the maximum received power and scans to find an angular position of the RX, and during the scanning, the RX sends feedback information about the received power. For the most effective power transmission control, the TX system can determine a precise location of the RX based on the feedback information from the RX. However, the received power of the RX is not different for a different scanning angle, it is impossible to determine a precise location of the RX.
Accordingly, at present, the field of wireless power transmission is actively being developed and there are many solutions disclosing different aspects of the issues.
Taking a close look at one of the solutions, a system for providing wireless charging and/or primary power for electronic/electric devices through microwave energy, the microwave energy is focused to a location by a power transmitter having one or more adaptively-phased microwave array emitters. Rectennas within a device to be charged receive and rectify the microwave energy and use it for battery charging and/or for primary power. However, a transmitting unit can have many transceiver modules to operate both in transmitting and receiving modes to detect a receiver unit. During the latter mode, the transmitting unit can operate to detect a phase of a received signal at every element of the antenna array. Moreover, the aforementioned TX design assumes that the system can be able to maintain a single transmitting array element operation mode. The TX architecture is rather complex and can have at least two times more hardware elements than a single-mode transmitting unit. Also, how to simultaneously charge several receiving units may not be provided.
Another power system suggests a TX that transmits a power transmission signal (e.g., microwave signal waves) to create a three-dimensional pocket of energy. At least one RX may be connected to or integrated into electronic devices and may receive power from the pocket of energy. The TX may locate the at least one RX in a three-dimensional space using a communication medium (e.g., Bluetooth technology). The TX generates a waveform to create a pocket of energy around each of the at least one RX. The TX uses an algorithm to direct, focus, and control the waveform in three dimensions. The RX may convert the transmission signals (e.g., microwave signals) into electricity for powering an electronic device. Accordingly, the embodiments for wireless power transmission may allow powering and charging a plurality of electrical devices without wires. However, a search procedure for determining locations of power receivers in relation to the power transmitter is very long and not optimal, as it is based on iterative sorting of all phase states for each TX antenna element. Furthermore, multi-receiver charging can have TX antenna separation on several arrays, which leads to low efficiency of power transmission.